Distribution of catecholamines, serotonin, and their major metabolites in the rat cingulate, piriform-entorhinal, somatosensory, and visual cortex: a biochemical survey using high-performance liquid chromatography

Peripheral serotonin transporter DNA methylation is linked to increased salience network connectivity in females with anorexia nervosa

BACKGROUND

Epigenetic variation in the serotonin transporter gene (SLC6A4) has been shown to modulate the functioning of brain circuitry associated with the salience network and may heighten the risk for mental illness. This study is, to our knowledge, the first to test this epigenome–brain–behaviour pathway in patients with anorexia nervosa.

METHODS

We obtained resting-state functional connectivity (rsFC) data and blood samples from 55 acutely underweight female patients with anorexia nervosa and 55 age-matched female healthy controls. We decomposed imaging data using independent component analysis. We used bisulfite pyrosequencing to analyze blood DNA methylation within the promoter region of SLC6A4. We then explored salience network rsFC patterns in the group × methylation interaction.

RESULTS

We identified a positive relationship between SLC6A4 methylation levels and rsFC between the dorsolateral prefrontal cortex and the salience network in patients with anorexia nervosa compared to healthy controls. Increased rsFC in the salience network mediated the link between SLC6A4 methylation and eating disorder symptoms in patients with anorexia nervosa. We confirmed findings of rsFC alterations for CpG-specific methylation at a locus with evidence of methylation correspondence between brain and blood tissue.

LIMITATIONS

This study was cross-sectional in nature, the sample size was modest for the method and methylation levels were measured peripherally, so findings cannot be fully generalized to brain tissue.

CONCLUSION

This study sheds light on the neurobiological process of how epigenetic variation in the SLC6A4 gene may relate to rsFC in the salience network that is linked to psychopathology in anorexia nervosa.

Age-related changes in the visual cortex: a review

The main age related changes in visual cortex are reviewed. The visual cortex (occipital cortex, areas 17-19) undergoes a variety of anatomical, biochemical and functional changes with aging. From a morphological point of view the visual cortex loses nerve cells mainly in the last period of life. From a biochemical point of view cholinergic, serotonergic, and GABAergic neurotransmissions seem to be the most remarkably affected. In terms of functional correlates, a decline of several activities of the visual cortex has been documented in the elderly. Due to the importance of visual cortex in the realization of visual function, the influence of aging on this cerebrocortical area requires a more detailed analysis.

Biochemical and autoradiographic studies of the central noradrenergic system in dystonia musculorum mutant mice

The autosomal recessive mutation dystonia musculorum (dt(J)/dt(J)) causes degenerative alterations of peripheral and central sensory pathways leading to ataxia. To determine the consequences of this pathology on the central noradrenergic (NA) system, NA contents were measured by high-performance liquid chromatography (HPLC) in 22 brain regions and spinal cord, while NA transporters, or uptake sites, were evaluated by quantitative ligand binding autoradiography, using [3H]nisoxetine, in wild-type and dt(J)/dt(J) mutant mice. The only significant differences in NA contents between the two genotypes were increased levels in hypothalamus and mesencephalic dopaminergic regions A9/A10 of dt(J)/dt(J) mutants. The dt(J)/dt(J) spinal cord showed a similar result, but its NA content remained unchanged when taking into account its reduced volume. Binding to NA transporters revealed increased densities in sensory nuclei of cranial nerves, granular layer of the cerebellar cortex, as well as in cerebellar-related and basal ganglia structures, such as the lateral cuneate nucleus, pontine nuclei, substantia nigra, pontine reticular formation, median raphe nucleus and superior colliculus. Forebrain regions were relatively unaffected in the dt(J)/dt(J) mutants, although NA transporter densities were higher in piriform cortex, hippocampal subdivisions and ventro-anterior thalamic nucleus. In contrast, densities of NA transporters were decreased in hypothalamic subregions and in two ventrobasal thalamic nuclei. The results are discussed in relation to expression of the dystonin gene in normal brain, cellular defects resulting from the loss of gene transcription in the dt(J)/dt(J) mutation, functional circuits of the central nervous system and some of the phenotypical characteristics of dystonia musculorum mutants.

Prenatal cocaine exposure produces consistent developmental alterations in dopamine-rich regions of the cerebral cortex

Administration of cocaine to pregnant rabbits produces robust and long-lasting anatomical alterations in the dopamine-rich anterior cingulate cortex of offspring. These effects include increased length and decreased bundling of layer III and V pyramidal neuron dendrites, increases in parvalbumin expression in the dendrites of interneurons, and increases in detectable GABAergic neurons. We have now examined multiple cortical regions with varying degrees of catecholaminergic innervation to investigate regional variations in the ability of prenatal cocaine exposure to elicit these permanent changes. All regions containing a high density of tyrosine hydroxylase-immunoreactive fibers, indicative of prominent dopaminergic input, exhibited alterations in GABA and parvalbumin expression by interneurons and microtubule-associated protein-2 labeling of apical dendrites of pyramidal neurons. These regions included the medial prefrontal, entorhinal, and piriform cortices. In contrast, primary somatosensory, auditory and motor cortices exhibited little tyrosine hydroxylase staining and no measurable cocaine-induced changes in cortical structure. From these data we suggest that the presence of dopaminergic afferents contributes to the marked specificity of the altered development of excitatory pyramidal neurons and inhibitory interneurons induced by low dose i.v. administration of cocaine in utero.

Pharmacology and behavioral pharmacology of the mesocortical dopamine system

The prefrontal cortex (PFC) has long been known to be involved in the mediation of complex behavioral responses. Considerable research efforts are directed towards refining the knowledge about the function of this brain area and the role it plays in cognitive performance and behavioral output. In the first part, this review provides, from a pharmacological perspective, an overview of anatomical, electrophysiological and neurochemical aspects of the function of the PFC, with an emphasis on the mesocortical dopamine system. Anatomy of the mesocortical system, basic physiological and pharmacological properties of neurotransmission within the PFC, and interactions between dopamine and glutamate as well as other transmitters within the mesocorticolimbic circuit are included. The coverage of these data is largely restricted to what is relevant for the second part of the review which focuses on behavioral studies that have examined the role of the PFC in a variety of phenomena, behaviors and paradigms. These include reward and addiction, locomotor activity and sensitization, learning, cognition, and schizophrenia. Although the focus of this review is on the mesocortical dopamine system, given the intricate interactions of dopamine with other transmitter systems within the PFC and the importance of the PFC as a source of glutamate in subcortical areas, these aspects are also covered in some detail where appropriate. Naturally, a topic as complex as this cannot be covered comprehensively in its entirety. Therefore this review is largely limited to data derived from studies using rats, and it is also specifically restricted to data concerning the medial PFC (mPFC). Since in several fields of research the findings concerning the function or role of the mPFC are relatively inconsistent, the question is addressed whether these inconsistencies might, at least in part, be related to the anatomical and functional heterogeneity of this brain area.

Altered serotonin and dopamine metabolism in the CNS of serotonin 5-HT(1A) or 5-HT(1B) receptor knockout mice

Measurements of serotonin (5-HT), dopamine (DA), and noradrenaline, and of 5-HT and DA metabolites, were obtained by HPLC from 16 brain regions and the spinal cord of 5-HT(1A) or 5-HT(1B) knockout and wild-type mice of the 129/Sv strain. In 5-HT(1A) knockouts, 5-HT concentrations were unchanged throughout, but levels of 5-HT metabolites were higher than those of the wild type in dorsal/medial raphe nuclei, olfactory bulb, substantia nigra, and locus coeruleus. This was taken as an indication of increased 5-HT turnover, reflecting an augmented basal activity of midbrain raphe neurons and consequent increase in their somatodendritic and axon terminal release of 5-HT. It provided a likely explanation for the increased anxious-like behavior observed in 5-HT(1A) knockout mice. Concomitant increases in DA content and/or DA turnover were interpreted as the result of a disinhibition of DA, whereas increases in noradrenaline concentration in some territories of projection of the locus coeruleus could reflect a diminished activity of its neurons. In 5-HT(1B) knockouts, 5-HT concentrations were lower than those of the wild type in nucleus accumbens, locus coeruleus, spinal cord, and probably also several other territories of 5-HT innervation. A decrease in DA, associated with increased DA turnover, was measured in nucleus accumbens. These changes in 5-HT and DA metabolism were consistent with the increased aggressiveness and the supersensitivity to cocaine reported in 5-HT(1B) knockout mice. Thus, markedly different alterations in CNS monoamine metabolism may contribute to the opposite behavioral phenotypes of these two knockouts.

Repeated ethanol administration induces short- and long-term changes in enkephalin and dynorphin tissue concentrations in rat brain

Recently, we have shown that rats repeatedly treated with ethanol and/or cocaine have decreased kappa-opioid receptor mRNA levels in the mesolimbic system. The aim of the present study was to investigate the short- and long-term effects of repeated ethanol administration on opioid peptide concentrations in brain tissue of male Sprague-Dawley rats. Dynorphin B (1-13) (Dyn B) and Met-enkephalinArg(6)Phe(7) (MEAP), endogenous ligands to kappa- and delta-opioid receptors, respectively, were measured using radioimmunoassays. The rats were given either ethanol [intraperitoneal (ip), twice daily, 2 g/kg bw/dose] or saline for 13 consecutive days. Thirty minutes after the last ethanol dose on Day 13, the Dyn B tissue concentration was significantly decreased in the cingulate cortex. The MEAP tissue concentration was decreased in the hippocampus 5 days after the last ethanol injection as compared to saline-treated controls. Furthermore, the Dyn B and the MEAP concentrations were increased in the periaqueductal grey area (PAG) at this time point. Of particular interest were the significant increases in Dyn B tissue concentrations found in the nucleus accumbens (NAcc) at 30 min and at 21 days after the last ethanol dose. The results suggest that repeated ethanol administration induces both short- and long-term changes in the tissue concentrations of opioids in certain brain regions associated with motivation and reward.

Central serotonin system in Dystonia musculorum mutant mice: biochemical, autoradiographic and immunocytochemical data

The autosomal recessive mutation dystonia musculorum (dt(J)/dt(J)) causes degenerative alterations of peripheral and central sensory pathways that lead to ataxia. To investigate possible changes in the central serotonin system of these mice, HPLC measurements of 5-hydroxytryptophan, 5-hydroxy-tryptamine (serotonin; 5-HT), and 5-HT metabolites were obtained from 22 brain regions and the spinal cord of wild type and dt(J)/dt(J) mutant mice. Also, 5-HT transporters were quantified by [(3)H]citalopram autoradiography in 72 brain regions, subregions, and nuclei, and the 5-HT innervation visualized by immunocytochemistry throughout the brain and spinal cord. In all brain regions measured for indoleamine content, there were no significant differences between the two genotypes. In the spinal cord, an increased tissue concentration of 5-HT (+34%), 5-hydroxyindole-3-acetic acid (+33%), 5-hydroxytryptophol (+21%), and 5-hydroxytryptophan (+45%) in dt(J)/dt(J) actually corresponded to the same total amount of each of these indoleamines in the entire spinal cord, when taking into account its reduced size in the mutants. Quantification of the binding to 5-HT transporters showed increases in the medial geniculate nucleus (+14%), medial (+24%) and lateral (+18%) hypothalamus, interpeduncular (+13%), vestibular (+22%), and deep cerebellar nuclei (+37%) of dt(J)/dt mice, and decreases in the ventral tegmental area (-13%), median and linear raphe nuclei (-20%), as well as in the solitary complex (-35%). There were no apparent differences in the distribution of 5-HT-immunostained fibers in these and other regions of brain and in the spinal cord of dt(J)/dt(J) compared to wild type mice. The bulk of these results indicates a relative sparing of the central 5-HT system in the dt(J)/dt(J) mice, even though alterations in 5-HT transporters could justify attempts at improving the sensorimotor dysfunction by administration of serotoninergic agents in these mice.

Dopamine D(1) and D(2) receptors in the forebrain of dystonia musculorum mutant mice: an autoradiographic survey in relation to dopamine contents

Dystonia musculorum (dt(J)/dt(J)) mutant mice suffer from a degeneration of spinocerebellar tracts as well as a dystrophy of peripheral sensory tracts. This neurological mutant has been proposed as an animal model of human cerebellar ataxia, in particular of the Friedreich's type; thus, it was deemed of interest to examine the endogenous contents of dopamine (DA) and metabolites as well as the distribution of DA receptors of the D(1) and D(2) subtypes, in order to delimit the biochemical characteristics of this pathological disorder, and determine an eventual dopaminergic dysfunction in this mutant. Tissue DA and its major metabolites 3, 4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine were measured by HPLC coupled to electrochemical detection in six cortical regions, in four divisions of rostral neostriatum and two halves of caudal neostriatum, as well as in olfactory bulb, nucleus accumbens, septum, amygdala, hippocampus, thalamus, hypothalamus, brainstem, cerebellum, substantia nigra, and ventral tegmental area. The only significant difference between dt(J)/dt(J) mice and wild-type controls was an increase in hypothalamic DA contents (+47%). Quantitative autoradiography with [(3)H]SCH23390 and [(3)H]raclopride, to label D(1) and D(2) receptors, respectively, revealed only moderate changes in receptor densities in a few localized regions. In dt(J)/dt(J) mutants, D(1) receptor numbers were found to be higher in thalamus (+27%) as well as in the medio-dorsal (+16%) and in the latero-dorsal (+16%) quadrants of rostral neostriatum, while D(2) receptor densities were greater in the medio-ventral (+32%) and the latero-dorsal (+17%) quadrants. The present results indicate an overall conservation of dopaminergic functions, albeit the few localized sites of increased D(1) and D(2) receptor densities, and that are seemingly independent of the DA innervation pattern, as revealed by the tissue measurements of DA and metabolites. They also rule out a major pathology linked to deficits in DA neurotransmission, and validate this mutant as an animal model of human cerebellar ataxia, probably of the Friedreich type.

Effects of buspirone on brain indoleamines and catecholamines in wild-type mice and Lurcher mutants

The effects of a chronic serotoninergic stimulation on brain monoamine levels and metabolism were studied in wild-type (+/+) mice and Lurcher (Lc/+) mutants. Endogenous serotonin, dopamine, noradrenaline and some of their major metabolites were measured in the frontal cortex, neostriatum, thalamus, brainstem, cerebellum and spinal cord. In +/+ mice, buspirone (1 mg/kg; i.p.) treatment during 40 days increased indoleamines, albeit with moderate changes in the ratios between tissue serotonin metabolites and endogenous serotonin, augmented noradrenaline contents in the spinal cord, and caused elevations of dopamine metabolites in most regions. In Lc/+ mutants, the effects of buspirone were attenuated, but higher L-tryptophan and indoleamine levels, suggest a storage of serotonin in a non-releasable compartment. In the hypoplastic Lc/+ cerebellum, indoleamine content was accrued, but with a decreased [serotonin metabolites]/[serotonin] ratio, indicating that the reorganized nerve terminals in Lc/+ mutants although they can synthesize and accumulate serotonin, may not utilize it efficiently in synaptic transmission.

Differential effects of L-trytophan and buspirone on biogenic amine contents and metabolism in Lurcher mice cerebellum

The effects of serotoninergic stimulation on monoamines were studied in the heterozygous Lurcher (Lc/+) mutant mouse, a model of human cerebellar ataxia. Wild type (+/+) and Lc/+ mice were treated for 40 days with L-tryptophan or buspirone, and serotonin (5-HT), dopamine (DA), noradrenaline (NA) and their main metabolites were measured in the cerebellum. In +/+ mice, only buspirone increased concentrations of 5-HT metabolites. In the hypoplastic Lc/+ cerebellum, indoleamines were higher, and increased further after both treatments. The 5-HT turnover index was increased in +/+ mice by buspirone, while in Lc/+ mutants it increased after L-tryptophan but was decreased by buspirone, indicating that in the mutants nerve terminals synthesize and accumulate 5-HT, but may not utilize it efficiently. Catecholamine contents remained unchanged in +/+ mice, but in Lc/+ mutants with higher endogenous NA, L-tryptophan further increased NA and 3,4-dihydroxy-phenylacetic acid (DOPAC), and buspirone augmented NA, DA and DOPAC levels.

Distribution of dopamine, its metabolites, and D1 and D2 receptors in heterozygous and homozygous weaver mutant mice

In weaver mice, besides a postnatal cerebellar developmental anomaly probably caused by alterations of an inwardly rectifying K+ channel, there is a progressive loss of mesencephalic dopaminergic neurons. To further evaluate this deficit, endogenous dopamine and its metabolites were measured in 22 brain regions from heterozygous (wv/+) and homozygous (wv/wv) mutants, and compared to wild type (+/+) mice. In both wv/+ and wv/wv mutants there were profound dopamine depletions in all regions; these changes were accompanied by decreases in metabolites but with an increase of turnover indexes. Dopamine D1 and D2 receptors were examined by autoradiography, and their distribution was conserved. The results show that the dopaminergic deficit is widespread to all areas of innervation, and is probably compensated for by an increased turnover. Abnormal developmental growth signals, or aberrant cellular responses, may result in defective neurite formation of the midbrain dopaminergic neurons, leading to their postnatal death.

Regional distribution of 5-HT transporters in the brain of wild type and 'Purkinje cell degeneration' mutant mice: a quantitative autoradiographic study with [3H]citalopram

The neurological mutant 'Purkinje cell degeneration' (pcd) is characterized by a primary degeneration of Purkinje cells, as well as by retrograde and secondary partial degeneration of cerebellar granule cells and inferior olivary neurons, and can be considered as an animal model of human degenerative ataxias. The serotonin (5-HT) innervation was examined in wild type and pcd mice, by quantifying 5-HT uptake sites, or transporters, using [3H]citalopram binding autoradiography. In both wild type and pcd mutants, the highest densities of 5-HT transporters were in mesencephalic and rostral pontine regions, in limbic structures, in hypothalamus and in discrete thalamic divisions, while the lowest labelling was found in cerebellum and brainstem reticular formation. In pcd mice, although [3H]citalopram labelling was higher in cerebellar cortex and deep cerebellar nuclei, when binding densities were corrected for surface area, the up-regulation of 5-HT transporters was present only in deep cerebellar nuclei. Also, higher labelling was found in nuclei raphe dorsalis and medialis, in ventral divisions of rostral neostriatum, caudal neostriatum, rostral globus pallidus, posteromedial amygdaloid nucleus, septum, olfactory tubercles, vertical limb of Broca's diagonal band, periventricular, latero-ventral and medio-ventral thalamic nuclei, medial geniculate nucleus, anterior hypothalamus and entorhinal cortex. The results indicate a relative integrity of the 5-HT innervation, but with a reorganization of serotoninergic terminals in the cerebellum, in particular in the deep cerebellar nuclei. This suggests that in progressive cerebellar degeneration, as found in the pcd mutant, the modified 5-HT system may still participate in motor functions by exerting an overall modulation of excitatory amino acid neurotransmission, but the availability of 5-HT may be altered in defined brain targets, as is the case for other spontaneous cerebellar mutants, in particular for the 'Lurcher' mutant mouse, a model of human olivopontocerebellar atrophy.

Functional evidence that BDNF is an anterograde neuronal trophic factor in the CNS

In this report, we have tested the hypothesis that brain-derived neurotrophic factor (BDNF) is an anterograde neurotrophic factor in the CNS and have focused on central noradrenergic neurons that synthesize BDNF. Double-label immunocytochemistry for BDNF and dopamine-beta-hydroxylase (DBH), a marker for noradrenergic neurons, demonstrated that BDNF is partially localized to noradrenergic nerve fibers and terminals in the adult rat brain. To test the functional importance of this anterograde BDNF, we analyzed transgenic mice carrying a DBH-BDNF minigene. Increased synthesis of BDNF in noradrenergic neurons of DBH-BDNF mice caused elevated TrkB tyrosine kinase activation throughout postnatal life in the neocortex, a noradrenergic target region. This afferently regulated increase in TrkB receptor activity led to long-lasting alterations in cortical morphology. To determine whether noradrenergic neuron-expressed BDNF also anterogradely regulated neuronal survival, we examined a second noradrenergic target, neonatal facial motoneurons. One week after axotomy, 72% of facial motoneurons were lost in control animals, whereas only 30-35% were lost in DBH-BDNF transgenic mice. Altogether, these results indicate that BDNF is anterogradely transported to fibers and terminals of noradrenergic neurons, that anterogradely secreted BDNF causes activation of TrkB in target regions, and that this secretion has functional consequences for target neuron survival and differentiation. This presynaptic secretion of BDNF may provide a cellular mechanism for modulating neural circuitry, in either the developing or mature nervous system.

Effects of a chronic lithium treatment on cortical serotonin uptake sites and 5-HT1A receptors

The objectives of this study were to characterize the effects of a chronic lithium (Li+) treatment on serotonin (5-HT) uptake sites and on 5-HT1A receptors, and to determine the eventual reversibility of the treatment. The experiments were carried out with membranes from rat cerebral cortex using 8-hydroxy-2-(propylamino)tetralin, or [3H]8-OH-DPAT, and [3H]citalopram to label 5-HT1A receptors and 5-HT uptake sites, respectively. Endogenous levels of 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) were measured by high-performance liquid chromatography in the cingulate cortex. The saturation curves with [3H]8-OH-DPAT were always best fitted a two-site model. After a treatment with Li+ for 28 days, no alterations in the binding parameters of [3H]8-OH-DPAT to the high- and low-affinity binding sites could be documented. However, competition curves with 5-HT to inhibit [3H]8-OH-DPAT binding revealed a decreased proportion of sites with high affinity for the agonist, together with an increased density of sites with low affinity for 5-HT, suggesting an alteration in the coupling efficacy between 5-HT1A receptors and their transduction systems. Saturation studies with [3H]citalopram showed an increase (> 40%) in the density of 5-HT uptake sites after chronic Li+, suggesting a more efficient 5-HT uptake process for the treated animals, in accord with clinical observations. Although 5-HT contents in cingulate cortex remained unchanged after the treatment, 5-H[AA levels decreased (> 30%), leading to a diminished (almost 50%) 5-HT turnover; and also reflecting a more efficient uptake in the treated rats, so that less 5-HT could be degraded by extracellular monoamine oxidase. All the effects revealed by [3H]8-OH-DPAT and [3H]citalopram were reversed following a recovery period of two days without Li+. Since symptoms of bipolar affective disorders may reappear if the chronic Li+ treatment is interrupted, the reversibility of the observed effects further supports the importance of central 5-HT synaptic transmission in the pathophysiology and treatment of human affective disorders.

Regional distribution of the 5-HT innervation in the brain of normal and lurcher mice as revealed by [3H]citalopram quantitative autoradiography

The neurological cerebellar mutant lurcher is characterized by a primary degeneration of Purkinje cells as well as retrograde secondary partial degeneration of cerebellar granule cells and inferior olivary neurons. Since serotonin (5-HT) has been implicated in the modulation of excitatory amino acid systems of the cerebellum, the 5-HT innervation of the normal and lurcher mice was examined by quantifying uptake sites using [3H]citalopram autoradiography, and by biochemical assays of the indoles 5-HT, 5-hydroxy-L-tryptophan and 5-hydroxyindole-3-acetic acid using high-performance liquid chromatography. Comparable results were found between [3H]citalopram binding and 5-HT tissue concentrations in different brain regions. The highest [3H]citaslopram labelling was observed in defined structures of the mesencephalic and upper pontine regions, in limbic strutures, in hypothalamus and in discrete thalamic divisions, while the lowest labelling of uptake sites was documented in cerebellum and brainstem reticular formation. In lurcher mutants, the histology confirmed cell degeneration and the reduction in width, leading to 65%, 45% and 25% atrophies of total cerebellum, deep nuclei and inferior olivary nucleus, respectively. The [3H]citalopram labelling corrected for surface loss was 45% and 20% higher to cerebellar deep nuclei and red nucleus, respectively, but remained unchanged in the cerebellar cortex and inferior olivary nucleus. Moreover, higher labelling was found in nucleus raphe dorsalis, ventral tegmental area, inferior colliculus, locus coeruleus, pontine central grey and anterior thalamic nuclei, areas known to be part of cerebellar afferent and efferent systems. The present results indicate that in such pathological conditions as described for the lurcher mutant, the 5-HT system may modulate motor function not only at the level of the cerebellum, but also in other forebrain structures functionally related to the motor system.

Catecholamine innervation of the piriform cortex: a tracing and immunohistochemical study in the rat

In order to determine the origin of the catecholamine innervation of the rat piriform cortex (PC), we combined retrograde transport of the B subunit of the cholera toxin (CTb) with tyrosine hydroxylase (TH) immunohistochemistry. A substantial number of CTb retrogradely labeled cells was found in the parabrachial pigmented, paranigral and interfascicular nuclei of the ventral tegmental area and the dorsal part of the locus coeruleus, whereas nearly no labeling was noted in the substantia nigra. Following TH immunohistochemistry on the same sections, most if not all of the CTb labeled cells were also TH immunoreactive. Occasional double-labeled cells were also observed in the anterior part of the raphe dorsal nucleus. As visualized with dopamine beta-hydroxylase, dopamine or TH immunohistochemistry, the noradrenaline fibers were homogeneously distributed whereas the dopamine fibers showed rostro-caudal and latero-medial differences. The distribution of TH fibers overlapped both patterns. Our report suggests that the heterogeneous distribution of the DA fibers could support a differential centrifugal modulation of the olfactory information processing throughout the PC.

Visual hallucinosis: the major clinical determinant of distorted chromatic contour perception in Parkinson's disease

Recently distorted chromatic contour perception has been demonstrated in Parkinson's disease (PD). The aim of our study is to determine the clinical factors which influence chromatic contour perception in PD. Chromatic and achromatic contour perception, colour discrimination and clinical data were evaluated in 73 patients with PD. We used a computer-aided method to determine the chromatic fusion time (CFT) which indicates the acuity of monochromatic contour perception. Chromatic CFT was generally shortened in patients as compared to controls (p < 0.01), whereas achromatic CFT was not significantly different. Variance analysis revealed the ability of colour discrimination and the risk of visual hallucinations as statistically significant (p < 0.05) variables influencing contour perception of certain stimuli. In contrast, disease stage, disease duration and disease severity have no relevant effect on chromatic contour perception in Parkinson's disease. On the basis of those properties one may suggest that distorted chromatic contour perception is due to an impairment at a central stage of visual processing in PD and an imbalance of the serotonergic system. Whether CFT is a reliable method to predict the individual risk of hallucinosis in PD has to be evaluated.

Serotonergic and non-serotonergic projections from the raphe nuclei to the piriform cortex in the rat: a cholera toxin B subunit (CTb) and 5-HT immunohistochemical study

Retrograde axonal transport of the cholera toxin B subunit (CTb) was combined with 5-HT immunohistochemistry to determine the origin of the serotonergic innervation of the piriform cortex (PC) in the rat. After iontophoretic CTb injections in the PC, a substantial number of retrogradely labeled cells were found in the middle and medio-ventral part of the dorsal raphe nucleus (RD). A few retrogradely labeled cells were also observed in the median raphe nucleus (MnR) and the B9 serotonergic cell groups. Following CTb and 5-HT immunohistochemistry on the same sections, double-labeled cells were observed in the RD, MnR and B9 groups. In the RD, 30% of CTb stained cells were immunoreactive to 5-HT. After colchicine or nialamide (a monoamine oxidase inhibitor) pretreatment the percentage of these double-labeled cells reached 70%. These results indicate that both 5-HT and non-5-HT neurons in the RD innervate the PC and that the percentage of double-labeled cells is influenced by drug pretreatment. To determine the terminal fields of the RD efferent fibers in the PC, injections of the anterograde tracer PHA-L were also performed. Analysis of the fiber distribution in the PC further revealed some medio-lateral and antero-posterior differences.

Regional alterations of dopamine and its metabolites in rat brain following portacaval anastomosis

Hyperammonemia and changes in brain monoamine metabolism have been proposed to contribute to the pathogenesis of the neuropsychiatric symptoms characteristic of human portal-systemic encephalopathy (PSE) resulting from chronic liver disease. Portacaval anastomosis (PCA) in the rat leads to sustained hyperammonemia and mild encephalopathy. In order to evaluate the role of dopamine (DA) metabolism in PSE, levels of DA and its metabolites were measured by HPLC with electrochemical detection in brain regions of rats with PCA at various stages of encephalopathy precipitated by ammonium acetate administration. Following ammonium acetate administration, rats with PCA rapidly develop severe neurological signs of encephalopathy progressing through loss of righting reflex to coma; sham-operated control animals administered ammonium acetate showed no such neurological deterioration. Concentrations of the DA metabolites DOPAC and HVA as well as [DA metabolites]/[DA] ratios, an indirect measure of DA turnover in brain, were increased in caudate-putamen, in cingulate and pyriform entorhinal cortices as well as in raphe nucleus and locus coeruleus. Increased DA metabolites, however, did not worsen at coma stages of PSE. Increased DA turnover thus appears to relate to early neuropsychiatric and extrapyramidal symptoms of PSE.

Dopamine and serotonin turnover rate in the retina of rabbit, rat, goldfish, and Eugerres plumieri: light effects in goldfish and rat

The concentration of dopamine, and its metabolites 3,4-dihydroxyphenylacetic and homovanillic acids, as well as serotonin and its metabolite 5-hydroxyindoleacetic acid, were determined in the retina of two teleosts, C. auratus (goldfish) and E. plumieri (mojarra), and two mammals, R. norvegicus (rat) and O. cuniculus (rabbit). The turnover rate of these monoamines were investigated in the four species by the calculation of the ratio monoamine/metabolite as an indirect index, and in goldfish and rat by the inhibition of the synthesis with alpha-methyl-p-tyrosine or p-chlorophenylalanine, by the increase in dopamine or serotonin by the corresponding precursors, 3,4-dihydroxyphenylalanine or 5-hydroxytryptophan, and by inhibition of monoaminooxidase with pargyline. The modulation by light and dark stimulation was studied in the goldfish and the rat. Differences in the concentration and turnover rate were observed among the species. Serotonin concentration was higher in the teleosts. The administration of inhibitors of dopamine and serotonin synthesis differentially decreased the levels of the monoamines in the retina of goldfish and rat. The rate of formation of dopamine and serotonin by the corresponding precursors was much higher in the goldfish than in the rat. Pargyline administration decreased 3,4-dihydroxyphenylacetic and 5-hydroxyindoleacetic acids at different rates and time dependency in the retina of goldfish and rat. Dopamine and serotonin concentration did not exhibit high modifications by the inhibitor, suggesting the function of regulatory mechanisms or additional effect of pargyline at other sites different from monoaminooxidase.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypersensitivity to serotonin and its agonists in serotonin-hyperinnervated neostriatum after neonatal dopamine denervation

Neonatal destruction of the nigrostriatal dopamine projection by intraventricular 6-hydroxydopamine leads to a serotonin (5-hydroxytryptamine, 5-HT) hyperinnervation of the adult neostriatum accompanied by increased radioligand binding to 5-HT1B, 5-HT1nonAB and 5-HT2 receptors. The consequences of such 5-HT receptor changes on neuronal responsiveness to 5-HT and corresponding receptor agonists were assessed with a quantitative iontophoretic approach. For comparative purposes, similar data were also obtained from rats 6-hydroxydopamine lesioned as adults, showing severe neostriatal dopamine denervation but no 5-HT hyperinnervation. In controls, 5-HT and its receptor agonists, m-chlorophenylpiperazine (mCPP; 5-HT1B/2C agonist) and dimethoxy-iodophenyl-aminopropane (DOI; 5-HT2A/2C agonist), depressed the firing rate of a majority of the unit tested. Three months after neonatal 6-hydroxydopamine lesion (5-HT-hyperinnervated tissue), inhibitory responses to all three agents were significantly increased and comparable results were obtained for 5-HT and DOI in the rostral versus caudal neostriatum. After 6-hydroxydopamine lesion in adults, neither responsiveness to 5-HT, mCPP or DOI nor the density of 5-HT1B or 5-HT2A binding were significantly different from control. Thus, the up-regulation of 5-HT1B, 5-HT2A and possibly 5-HT2C receptors accompanying the 5-HT hyperinnervation after neonatal but not after adult dopamine denervation was associated with increased responsiveness (IT50) of neostriatal neurons to iontophoresed 5-HT and its receptor agonists. Under these conditions, neostriatal 5-HT transmission might be enhanced in spite of a basal release seemingly comparable to normal (Jackson and Abercrombie, 1992, J. Neurochem. 58, 890).(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of cortical and hippocampal 5-HT1A receptors: a reappraisal of homogenate binding with 8-[3H]hydroxydipropylaminotetralin

The selective serotonin (5-HT) agonist 8-hydroxydipropylaminotetralin (8-OH-DPAT) has been extensively used to characterize the physiological, biochemical, and behavioral features of the 5-HT1A receptor. A further characterization of this receptor subtype was conducted with membrane preparations from rat cerebral cortex and hippocampus. The saturation binding isotherms of [3H]8-OH-DPAT (free ligand from 200 pM to 160 nM) revealed high-affinity 5-HT1A receptors (KH = 0.7-0.8 nM) and low-affinity (KL = 22-36 nM) binding sites. The kinetics of [3H]8-OH-DPAT binding were examined at two ligand concentrations, i.e., 1 and 10 nM, and in each case revealed two dissociation rate constants supporting the existence of high- and low-affinity binding sites. When the high-affinity sites were labeled with a 1 nM concentration of [3H]8-OH-DPAT, the competition curves of agonist and antagonist drugs were best fit to a two-site model, indicating the presence of two different 5-HT1A binding sites or, alternatively, two affinity states, tentatively designated as 5-HT1AHIGH and 5-HT1ALOW. However, the low correlation between the affinities of various drugs for these sites indicates the existence of different and independent binding sites. To determine whether 5-HT1A sites are modulated by 5'-guanylylimidodiphosphate, inhibition experiments with 5-HT were performed in the presence or in the absence of 100 microM 5'-guanylylimidodiphosphate. The binding of 1 nM [3H]8-OH-DPAT to the 5-HT1AHIGH site was dramatically (80%) reduced by 5'-guanylylimidodiphosphate; in contrast, the low-affinity site, or 5-HT1ALOW, was seemingly insensitive to the guanine nucleotide. The findings suggest that the high-affinity 5-HT1AHIGH site corresponds to the classic 5-HT1A receptor, whereas the novel 5-HT1ALOW binding site, labeled by 1 nM [3H]8-OH-DPAT and having a micromolar affinity for 5-HT, may not belong to the G protein family of receptors. To further investigate the relationship of 5-HT1A sites and the 5-HT innervation, rats were treated with p-chlorophenylalanine or with the neurotoxin p-chloroamphetamine. The inhibition of 5-HT synthesis by p-chlorophenylalanine did not alter either of the two 5-HT1A sites, but deafferentation by p-chloroamphetamine caused a loss of the low-affinity [3H]8-OH-DPAT binding sites, indicating that these novel binding sites may be located presynaptically on 5-HT fibers and/or nerve terminals.

Serotonergic suppression of interhemispheric cortical synaptic potentials

The inhibitory effects of 5-hydroxytryptamine (5-HT) on interhemispheric and intracortical synaptic potentials in layer V neurons of the rat medial prefrontal (MFC) cortex were examined. Low concentrations (1-3 microM) of 5-HT selectively attenuated polysynaptic potentials that were similarly evoked by callosal or white matter stimulation. Maximally effective concentrations of 5-HT blocked interhemispheric transmission by 50-90%, as evidenced by an attention of the short latency callosal depolarizing synaptic potential (e-DPSP). These effects of 5-HT were not associated with a change in membrane potential or input resistance. The e-DPSP was characterized as having an N-methyl-D-aspartate (NMDA) and a non-NMDA component; the non-NMDA component was attenuated by 5-HT. Attenuation of the synaptic potential was accompanied by an attenuation of a postsynaptic glutamate potential. Suppression of both the e-DPSP and the glutamate potential was concentration dependent with 10-100 microM being maximally effective. The 5-HT1A/2 antagonist, spiperone, antagonized the effects of 5-HT on synaptic and glutamate potentials. Spiperone (1 microM) shifted the concentration-effect curves for suppression of the e-DPSP and the glutamate potential to the right; however, the Kb for the glutamate potential concentration-effect curve was 10 times that for the e-DPSP curve. The differential antagonist sensitivity of synaptic and glutamate potentials was an indication that serotonin acted on more than one receptor subtype to reduce interhemispheric transmission.

6-Hydroxydopamine lesions of the medial prefrontal cortex of rats do not affect dopamine metabolism in the basal ganglia at short and long postsurgical intervals

Dopamine (DA) in the medial prefrontal cortex (mPFC) has been implicated in the regulation of subcortical DA function. To further characterize the potential interaction between cortical and subcortical DA systems, the short- and long-term neurochemical consequences of 6-hydroxydopamine (6-OHDA) lesions of the mPFC of rats were investigated in the mPFC and in its subcortical target structures. 4 to 5, 10 to 12 and 32 to 36 days after infusion of 6-OHDA, DA was depleted to a larger extent than noradrenaline and serotonin. No lesion-induced changes of DA and its metabolites were detected in subcortical structures. These results show that prefrontal 6-OHDA lesions produce immediate and long lasting depletions of prefrontal monoamines, especially of DA, without increasing basal DA metabolism in the striatum and nucleus accumbens.

Platelet-induced vasomotion of isolated canine coronary artery in the presence of halothane or isoflurane

To determine the effect of 1.5 MAC of two volatile anesthetics (halothane and isoflurane) on platelet-induced contraction of canine coronary artery, isolated, denuded coronary rings were suspended between two stirrups, placed into organ chambers filled with an oxygenated Krebs-Ringer solution, and connected to an isometric force transducer. Human platelets were obtained from healthy donors and introduced into the organ chambers in increasing amounts to reach 20,50 and, 70 x 10(9) platelets/L. The tension generated in both the control and anesthetic-treated rings was recorded; only halothane reduced the tension induced by platelet activation in the organ chambers. In some experiments, aliquots of Krebs-Ringer solution were taken to determine the amount of 5-HT and TB2 released by 70 x 10(9) human platelets in the presence and absence of the anesthetics. Only halothane reduced TA2 production by the activated platelets. Finally, the contractile response of isolated denuded canine coronary artery rings to U46619, a thromboxane analog, was measured in the presence and absence of the anesthetics. Neither halothane nor isoflurane attenuated the response. In another series of experiments, in vitro platelet aggregation was induced by epinephrine, collagen, ADP, or arachidonic acid in the presence or absence of 1.5 MAC isoflurane or halothane. Both anesthetics significantly reduced the aggregation.

Changes of D1 and D2 receptors in adult rat neostriatum after neonatal dopamine denervation: quantitative data from ligand binding, in situ hybridization and iontophoresis

The specific binding of [3H]SCH23390 to D1 and of [3H]raclopride to D2 dopamine receptors was measured by autoradiography in the rostral and caudal halves of neostriatum and in the substantia nigra of adult rats subjected to near total destruction of nigrostriatal dopamine neurons by intraventricular 6-hydroxydopamine soon after birth. Three months after this lesion, [3H]SCH23390 binding (D1 receptors) was slightly but significantly decreased in the rostral neostriatum (22%), but unchanged in its caudal half and in the substantia nigra. In contrast, [3H]raclopride binding (D2 receptors) was considerably increased throughout the neostriatum (10-40%), while markedly decreased in the substantia nigra (80%). In the rostral neostriatum, there were no parallel changes in D2 receptor messenger RNA levels, as measured by in situ hybridization on adjacent sections. Caudally, however, slight but significant increases in D2 messenger RNA could be observed (10-20%). As assessed by quantitative iontophoresis, there was a marked enhancement (63%) of the inhibitory responsiveness of spontaneously firing units in the rostral neostriatum to dopamine and the D1 agonist, SKF38393, in neonatally lesioned compared to control rats. On the other hand, responsiveness to PPHT, a potent D2 agonist, appeared to be unchanged. Such opposite changes in the number of D1 and D2 binding sites, dissociated from the expression of D2 receptor messenger RNA and from the sensitivity to dopamine and D1 and D2 agonists, suggested independent adaptations of these various parameters following the neonatal dopamine denervation of neostriatum. They also provided further evidence for mechanisms other than the dopamine innervation in the control of the expression of neostriatal D2 receptor messenger RNA during ontogenesis, and emphasized that the effects of dopamine and its D1 and D2 agonists in neostriatum do not depend strictly on the number of D1 and D2 primary ligand recognition sites.

Distribution of indoleamines and [3H]paroxetine binding in rat brain regions following acute or perinatal delta 9-tetrahydrocannabinol treatments

The effects of delta 9-tetrahydrocannabinol (delta 9-THC) administration on the central serotoninergic system were evaluated by biochemical assays of tissue levels of indoleamines; a measure of the serotonin (5-HT) innervation was obtained by using [3H]paroxetine as a marker of 5-HT uptake sites. Two different delta 9-THC treatments were chosen, i.e.: acute and chronic perinatal maternal exposure. Following acute treatment (5 mg/kg), the 5-HT content increased in dorsal hippocampus (+35%), Substantia nigra (+61%) and neostriatum (+62%) but remained unchanged in cingulate cortex, Raphe nuclei, Locus coeruleus and anterior hypothalamus. Endogenous 5-hydroxyindole-3-acetic acid (5-HIAA) decreased in anterior hypothalamus (-23%) and Raphe nuclei (-21%). Following maternal exposure to delta 9-THC (5 mg/kg per day; from gestational day 13 to postnatal day 7), levels of 5-HT were increased in the neostriatum (+22%) but decreased in anterior hypothalamus (-25%), Raphe nuclei (-29%) and Locus coeruleus (-20%) of the litters. Tissue 5-HIAA was increased in anterior hypothalamus (+23%) and Substantia nigra (+48%). There were no changes in 5-HT uptake site density, determined by [3H]paroxetine binding, except for an increase (+50%) in the cingulate cortex of perinatal-treated rats when compared to acutely-treated animals. The present results show that acute and maternal exposure to delta 9-THC produced different effects on the central 5-HT system of the offspring, with a clear regional specificity, but with no changes in the densities of 5-HT uptake sites.

Changes of amino acid and monoamine levels after neonatal 6-hydroxydopamine denervation in rat basal ganglia, substantia nigra, and Raphe nuclei

The effects of a neonatal dopaminergic deafferentation with the neurotoxin 6-hydroxydopamine (6-OHDA) on endogenous tissue levels of catecholamines, indoleamines, and amino acids were investigated in discrete rat brain regions. After producing the lesion at postnatal day 3 by intraventricular injections of 6-OHDA, with a desipramine pretreatment to protect noradrenaline neurons, the animals were kept for 3 months. Their brains were dissected to obtain samples of neostriatum, Globus pallidus, Substantia nigra, and Raphe nuclei, which were then analyzed by high-performance liquid chromatography, coupled either to electrochemical detection for aromatic monoamines, or to post-column ninhydrin derivatization with spectrophotometry for amino acids. The neonatal 6-OHDA treatment depleted dopamine (DA) levels in neostriatum, Globus pallidus, and Substantia nigra, but in Raphe nuclei DA was increased. The main metabolites of DA were also decreased in neostriatum, Globus pallidus, and Substantia nigra but remained unchanged in Raphe nuclei. Serotonin (5-HT) and its metabolite 5-hydroxy-indole-3-acetic acid increased in neostriatum and Raphe nuclei; in Substantia nigra there was a slight increase in 5-HT only. The 6-OHDA lesion caused heterogeneous alterations in amino acid contents, which varied according to the region. In the neostriatum there were increases of gamma-aminobutyric acid (GABA), aspartic acid, and glycine. In the Globus pallidus taurine, GABA, glutamic acid, glutamine, aspartic acid, serine, and alanine were elevated. In the Substantia nigra only increases in taurine, GABA, glutamic acid, and glutamine could be documented. This study shows important changes in amino acid levels and in some of their ratios, occurring in different anatomical subdivisions of the basal ganglia and related brainstem nuclei following a neonatal treatment with 6-OHDA. The results thus demonstrate major biochemical modifications in amino acids in the aftermath of a DA denervation and/or a 5-HT hyperinnervation during an early developmental period.

[3H]paroxetine binding and serotonin content of rat brain: absence of changes following antidepressant treatments

The high affinity binding of [3H]paroxetine was measured in rat cerebral cortex following chronic treatment (21 days) with imipramine (5 mg/kg), trimipramine (5 mg/kg) and fluoxetine (2 mg/kg), in adult (3-4 months) or neonatal (7 days of age) rats. Tissue concentrations of serotonin and of its metabolite 5-hydroxyindole-3-acetic acid were also determined by high-performance liquid chromatography in cingulate cerebral cortex, rostral neostriatum, hippocampus and midbrain raphe nucleus region. No differences were found in any of the parameters of [3H]paroxetine binding after antidepressant administration, in either adult or neonatal animals. In addition, endogenous serotonin and 5-hydroxyindole-3-acetic acid levels were not different from control values in any of the regions examined. The present study shows that the serotonin uptake recognition site is resilient to changes after chronic treatment with therapeutic doses of antidepressants, and emphasizes the potential usefulness of uptake site ligands as markers to quantify innervation densities within the brain.

Serotonin 5-HT1 and 5-HT2 receptors in adult rat brain after neonatal destruction of nigrostriatal dopamine neurons: a quantitative autoradiographic study

Neonatal destruction of nigrostriatal dopamine neurons by cerebroventricular injection of 6-hydroxydopamine (6-OHDA) results in a serotonin (5-HT) hyperinnervation of the rostral neostriatum in adult rat. Quantitative ligand-binding autoradiography was used to compare the density of various 5-HT receptor subtypes in the adult brain of control and neonatally 6-OHDA-lesioned rats. 5-HT1A, 5-HT1B, 5HT1nonAB and 5-HT2 sites were labeled with [3H]8-OH-DPAT, [125I]cyanopindolol, [3H]5-HT and [125I]DOI, respectively, and measured in the rostral and caudal halves of neostriatum and selected forebrain or midbrain regions. 5-HT1A binding, measured after 6 months, was unchanged in all regions examined including the dorsal raphe nucleus. Three months after the lesion, 5-HT1B binding was increased throughout the neostriatum (30%), but also in the substantia nigra (50%) and globus pallidus (30%), suggesting an up-regulation and an increased axonal transport of these receptors in neostriatal projection neurons. 5-HT1nonAB binding was also increased throughout the neostriatum (40%) and in the substantia nigra (50%), but unchanged in the globus pallidus, as if this up-regulation preferentially involved striatonigral as opposed to striatopallidal neurons. 5-HT2 binding showed an even greater increase (60%), which was restricted to the rostral half of neostriatum and also seemed imputable to an up-regulation as heteroreceptors. Even though the exact cause(s) of these receptor increases could not be determined, their anatomical distribution suggested that they were somehow related to the initial dopamine denervation in the case of the 5-HT1B and 5-HT1nonAB receptors, and more tightly linked to the 5-HT hyperinnervation in the case of the 5-HT2 receptors. Such receptor changes could participate in adaptive mechanisms implicating other transmitters and behavioral disturbances observed in this particular experimental model. Interestingly, they could also account for an enhancement of neostriatal 5-HT function even in a condition where extracellular levels of 5-HT apparently remain normal because of increased uptake.

Amino acid levels and gamma-aminobutyric acidA receptors in rat neostriatum, cortex, and thalamus after neonatal 6-hydroxydopamine lesion

The amino acid gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in brain, and GABAergic neurons have been proposed to play a major role in basal ganglia physiology. In the neostriatum (caudate putamen), medium-sized aspiny interneurons, as well as neostriatal output neurons that project to several brain regions, use GABA as their neurotransmitter. Dopamine fibers arising from the substantia nigra represent a major input to the neostriatum where, besides their classic neurotransmitter role, they are seemingly involved in the regulation of amino acid neurotransmitter release. To further characterize the nature of some of the amino acid/dopamine interactions, selective dopaminergic deafferentations were produced in neonatal rats (3 days postnatal) by intraventricular administration of the neurotoxin 6-hydroxydopamine (6-OHDA); the noradrenergic neurons were protected by prior administration of desmethylimipramine. After a 3-month survival, levels of catecholamines, indoleamines, and amino acids were determined in cingulate cortex, thalamus, and neostriatum. In addition, GABAA receptors were measured in membrane preparations from these three regions, using the specific agonist [3H]muscimol. In the 6-hydroxydopamine-lesioned rats, levels of dopamine and its metabolites homovanillic acid, 3,4-dihydroxyphenylacetic acid, and 3-methoxytyramine were decreased, as expected, in cortex and neostriatum, but remained unmodified in thalamus. In all three regions, serotonin content was increased; its metabolite, 5-hydroxyindole-3-acetic acid, was also elevated, but only in cortex and neostriatum. The levels of GABA were increased in neostriatum and thalamus, but remained unmodified in cortex. Glycine was increased in all three regions examined. There were also increases of phosphatidylethanolamine and serine in thalamus, and of aspartic acid and alanine in neostriatum. The density of GABAA binding sites was increased in neostriatum, but remained unchanged in cortex and thalamus. The changes in amino acid levels and [3H]muscimol binding sites induced by a neonatal 6-hydroxydopamine treatment differ from those found after similar lesions in adult animals, possibly because of the plastic and synaptic rearrangements that can still occur during early postnatal development. The present results also demonstrate that adaptations occur in response to a dopaminergic deafferentation at an early age and that these exhibit a regional specificity.

Comparative biochemical pharmacology of central nervous system dopamine D1 and D2 receptors

The biochemical properties of central nervous system (CNS) dopamine (DA) D1 and D2 receptors were examined using the specific antagonists [3H]SCH23390 and [3H]raclopride, respectively. There is a different participation of sulfhydryl (-SH) and disulfide (-SS-) groups in the binding site and/or coupling to second messenger systems of D1 and D2 receptors. The ionic studies with [3H]SCH23390 showed slight agonist and antagonist affinity shifts for the D1 receptor. On the other hand, the D2 receptor is very sensitive to cations; even if lithium and sodium influence specific [3H]raclopride binding in a similar manner, there appear to be quantitative differences between these two ions that cannot be explained by surface charge mechanisms. The distribution of D1 and D2 receptors was heterogenous in both species, with the greatest densities in the neostriatum, where the highest concentrations of DA and metabolites were measured. Regions with low endogenous DA content (cerebral cortex and hippocampus) had lower densities of DA receptors. Furthermore, these binding sites were differentially localized within the various regions, and there were substantially more D1 than D2 receptors. The functional significance and heterogeneities in the distribution of D1 and D2 receptors can be related to dopaminergic innervation and turnover.

Preparation of an optimum mobile phase for the simultaneous determination of neurochemicals in mouse brain tissues by high-performance liquid chromatography with electrochemical detection

A systematic method is described for the optimization of a mobile phase for the simultaneous determination of 24 neurochemicals consisting of catecholamine, serotonin, their precursors and metabolites and related materials. This mobile phase contained sodium acetate (0.04 M), citric acid (0.01 M), sodium chloride (0.0126 M), sodium octyl sulfate (91 mg/l), tetrasodium EDTA (50 mg/l) and 10% (v/v) methanol. When this optimum mobile phase was applied to the analysis of brain tissues of the Swiss male mouse, twelve neurochemicals were quantified in the free state: tyrosine, L-beta-3,4-dihydroxyphenylanine, dopamine, 3,4-dihydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenylacetic acid, norepinephrine, 3-methoxy-4-hydroxyphenylglycol, DL-3,4-dihydroxymandelic acid, DL-4-hydroxy-3-methoxymandelic acid, serotonin, L-tryptophan, 5-hydroxyindole-3-acetic acid and DL-synephrine and normetanephrine, appearing as a fused peak. This fused peak was present on the chromatogram tracings of all the mouse brain tissues. The separable neurochemicals not found by this procedure in the Swiss male mouse tissues were DL-3,4-dihydroxyphenylglycol,5-hydroxytryptophan, epinephrine, DL-octopamine, metanephrine, deoxyepinephrine, homovanillyl alcohol, N-acetylserotonin, tyramine and 3-methyltyramine.

Lithium reduced synaptic transmission and increased neuronal excitability without altering endogenous serotonin, norepinephrine and dopamine in rat hippocampal slices in vitro

1. Extracellular field potentials were recorded in the CA1 pyramidal cell layer following stimulation of stratum radiatum in rat hippocampal slices during superfusion with different concentrations (1, 2, 5, 10, 20, and 30 mM) of lithium (Li+). Control slices were exposed similarly to choline (Ch+) or sodium (Na+). 2. At high concentrations (greater than or equal to 10 mM), Li+, Ch+ and Na+ reduced the amplitude of the field excitatory postsynaptic potential (EPSP). However, Li+ increased, whereas Ch+ and Na+ reduced the population spike amplitude. Thus, Li+ specifically enhanced the excitability of CA1 pyramidal cells. 3. Electrophysiologically monitored slices, plus an additional group exposed to Li+, Ch+ or Na+ without concomitant field potential recordings, were processed for measurement of endogenous levels of serotonin (5-HT), norepinephrine (NE) and dopamine (DA). The mean endogenous levels of 5-HT and NE were not significantly different in 1-30 mM Li+, Ch+ and Na+. Dopamine contents were unchanged after exposure to Li+ and Na+, but were reduced by Ch+. 4. The non-specific effects of Li+ on synaptic transmission and its specific effects on neuronal excitability appeared independent of changes in endogenous 5-HT, NE and DA levels.

[3H]paroxetine binding and serotonin content of rat cortical areas, hippocampus, neostriatum, ventral mesencephalic tegmentum, and midbrain raphe nuclei region following p-chlorophenylalanine and p-chloroamphetamine treatment

The agents p-chlorophenylalanine (PCPA) and p-chloroamphetamine (PCA) deplete brain serotonin (5-HT) levels by two different mechanisms; PCPA inhibits the enzyme tryptophan hydroxylase, whereas PCA has a neurotoxic action on certain 5-HT neurons. The parameters of [3H]paroxetine binding to homogenates prepared from the cerebral cortex of rats treated with PCPA, PCA, or saline; vehicle were investigated. The tissue concentrations of 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) were also determined by HPLC in the same brain samples. After PCPA treatment, neither the maximum binding capacity (Bmax) nor the dissociation constant (KD) of [3H]paroxetine for the 5-HT uptake recognition site differed from controls despite a substantial reduction in the concentration of 5-HT and 5-HIAA. In contrast, significant changes in both the Bmax and KD values were observed in the cerebral cortex of rats treated with PCA. Furthermore, [3H]paroxetine binding and tissue concentrations of 5-HT and 5-HIAA were measured in the following different regions of the rat brain: cingulate, parietal, and visual cortical areas; dorsal and ventral hippocampus; rostral and caudal halves of neostriatum; ventral mesencephalic tegmentum; and midbrain raphe nuclei region after administration of PCPA, PCA, or saline vehicle. There was an excellent correlation between regional 5-HT levels and specific [3H]paroxetine binding in control and PCA-treated rats although this correlation was lost after PCPA treatment. Under these conditions, the 5-HT innervation remains unchanged whereas the concentration of 5-HT and 5-HIAA is greatly reduced. Thus, [3H]paroxetine binding appears to provide a reliable marker of 5-HT innervation density within the mammalian CNS.

[3H]paroxetine binding and serotonin content of rat and rabbit cortical areas, hippocampus, neostriatum, ventral mesencephalic tegmentum, and midbrain raphe nuclei region

The high-affinity binding of [3H]paroxetine to membranes was measured in different regions of the rat and rabbit brain: cingulate, frontal, parietal, piriform, entorhinal, and visual cortical areas; dorsal and ventral hippocampus; rostral and caudal halves of neostriatum (rat) or caudate nucleus and putamen (rabbit); ventral mesencephalic tegmentum; and midbrain raphe nuclei region. The tissue concentrations of serotonin (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxy-l-tryptophan (5-HTP) were also determined by high-performance liquid chromatography (HPLC) in the same brain samples. The regional density of [3H]paroxetine binding varied in both species; the highest values (Bmax) were found in the midbrain raphe region and ventral mesencephalic tegmentum. The cortical values ranged from moderate to low, with a significantly higher density in the cingulate cortex of the rat compared with rabbit. In the rat, there was also a higher density in the ventral than dorsal hippocampus, and the caudal than rostral neostriatum. In the rabbit, the hippocampal and neostriatal values were generally lower and more uniform. In both species, there was an excellent correlation between regional 5-HT levels and specific [3H]paroxetine binding (r = 0.87 in the rat and 0.96 in the rabbit). Considering the available quantitative data on the number of 5-HT nerve cell bodies and axon terminals in different regions of the rat brain, it appears likely that the high amount of [3H]paroxetine binding in the midbrain raphe region and ventral mesencephalic tegmentum reflects the presence of 5-HT uptake sites on 5-HT nerve cell bodies and dendrites as well as axon terminals. In other brain regions, the heterogeneous distribution of [3H]paroxetine binding parallels that of the number of 5-HT axon terminals, emphasizing the potential usefulness of this radioligand as a marker of 5-HT innervation density.

Elevation of dopamine D2 but not D1 receptors in adult rat neostriatum after neonatal 6-hydroxydopamine denervation

Monoamine levels and the binding properties of [3H]SCH23390, a D1-specific ligand, and [3H]raclopride, a D2-specific ligand, were measured in the rostal and caudal neostriatum to investigate the fate of dopamine receptors following bilateral cerebroventricular injection of 6-hydroxydopamine in 3-day-old rats. After survival times of 15, 30 or 90 days, measurement of monoamine levels and of [3H]SCH23390 binding were also obtained from the cerebral cortex. At all three survival times, dopamine content was reduced by more than 90% of control values in both the rostral and caudal neostriatum; in cerebral cortex, the dopamine depletion was less profound (80%) and noticeable only after 1 and 3 months. In the rostral but not the caudal neostriatum, serotonin and 5-hydroxyindoleacetic acid concentrations were markedly increased at 1 and 3 months; cortical serotonin also was augmented at 3 months. There were no changes in neostriatal [3H]SCH23390 binding at any of the survival times, but a transient elevation occurred in the cortex at 1 month. In the rostral but not the caudal neostriatum, [3H]raclopride binding showed a slight elevation at 1 month and a further, highly significant increase at 3 months. As measured in individual rats, this increase in [3H]raclopride binding was linearly correlated with the increase in serotonin turnover (ratio of 5-hydroxyindoleacetic acid/serotonin). Such an up-regulation of D2 receptors, restricted to the rostral neostriatum which was also the site of a serotonin hyperinnervation, was probably indicative of a serotonin control on the expression of D2 receptors after dopamine denervation.

Monoamines and their metabolites in somatosensory, visual, and cingulate cortices of adult rat: differences in content and lack of sidedness

Small areas of somatosensory, visual and cingulate cortex were microdissected and assayed for their monoamine content by high-performance liquid chromatography with electrochemical detection. No differences were found between the right and the left hemisphere for any area nor for any of the monoamines. The values averaged from left and right hemispheres for the sensory areas were significantly different from the cingulate in the content of norepinephrine, 4-hydroxy-3-methoxyphenylglycol, dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 5-hydroxy-1-tryptophan, serotonin and 5-hydroxyindole-3-acetic acid. The two sensory cortices differed in their levels of norepinephrine, dopamine, 3-4-dihydroxyphenylacetic acid and homovanillic acid. In the latter comparison, the measured amounts were higher in somatosensory than in visual cortex. This biochemical heterogeneity in monoamine distribution may reflect specific innervation patterns for these compounds in these discrete cortical areas and allows differences in content to be related to functional specializations of the cerebral cortex.

Effect of ammonia on brain serotonin metabolism in relation to function in the portacaval shunted rat

Four weeks following portacaval anastomosis (PCA) in the rat, severe liver atrophy, sustained hyperammonemia, and increased plasma and brain tryptophan are observed. Administration of ammonium acetate (NH4Ac) to rats with PCA precipitates severe signs of hepatic encephalopathy (HE) (loss of righting reflex progressing to loss of consciousness and ultimately deep coma). To evaluate the relationship between the deterioration of neurological status in HE and serotonin (5-HT) metabolism, the levels of 5-HT, its precursor 5-hydroxytryptophan, and its major metabolite 5-hydroxy-indole-3-acetic acid (5-HIAA) were measured by HPLC with ion-pairing and electrochemical detection in three well-defined areas of the cerebral cortex: anterior cingulate, piriform and entorhinal, and frontoparietal; as well as in the caudate-putamen, the raphe nuclei, and the locus ceruleus in rats with PCA at different stages of HE, before and after injection of NH4Ac, as well as in sham-operated controls. The results demonstrate increased 5-HIAA/5-HT ratios after PCA and NH4Ac loading, suggesting increased 5-HT turnover in the brains of these animals. However, these changes do not appear to be related to the precipitation of coma as no significant difference in 5-HT turnover was observed between precoma and coma stages of HE. Increased 5-HT turnover in brain of shunted rats may be related to early symptoms of HE such as altered sleep patterns and disorders of motor coordination.

Noradrenaline axon terminals in adult rat neocortex: an immunocytochemical analysis in serial thin sections

Peroxidase-antiperoxidase electron microscope immunocytochemistry with an antiserum against noradrenaline-glutaraldehyde-protein conjugate was used to identify cortical noradrenaline terminals (axonal varicosities) from the upper layers of the frontal, parietal and occipital cortex in adult rat. A large number of immunostained varicosities were examined in serial thin sections, and compared with a control population of randomly chosen unlabeled terminals from the same sections. Both groups of varicosities were measured and scrutinized for the presence of a junctional complex indicative of synaptic specialization. Cellular elements juxtaposed to the membrane of both types of varicosities were also identified and counted. Noradrenaline varicosities in all three cortical regions averaged 0.65 microns in diameter. In contrast to their unlabeled counterparts, these profiles rarely showed a membrane differentiation characteristic of a synaptic contact (junctional complex). The rare junctional complexes formed by cortical noradrenaline varicosities were invariably symmetrical and almost always found on dendritic shafts. The microenvironment of noradrenaline varicosities also differed, exhibiting a greater number of apposed axonal varicosities and a smaller number of dendritic spines than that of the random population. The proportion of noradrenaline varicosities making a synaptic contact (synaptic incidence) was determined by plotting the incidence of visible junctions as a function of the number of thin sections available for examination. As extrapolated for whole varicosities after linear transformation (double reciprocal plot), this proportion was 17% or 26% depending on the stringency of the criteria used in identifying the junctional complex. The same analysis provided a figure of 98% for the control population. The present study largely confirmed our initial radioautographic characterization of the cortical noradrenaline innervation as a mostly non-junctional system, and also indicated that these varicosities are set in a particular microenvironment. These new data further support the eventuality of a diffuse release of cortical noradrenaline in the extracellular space, compatible with both its neuromodulatory role and multiplicity of actions on diverse cellular targets in the cerebral cortex. The functions assigned to the coeruleocortical noradrenaline system must therefore be viewed as the product of a widespread and ubiquitously distributed neuronal organization characterized by loose intercellular relationships. This system might be capable of selectivity and specificity of action, however, owing to the distribution of its receptors, and in view of intrinsically or extrinsically driven control mechanisms triggered by the release of its own or other transmitters and which may also involve target-initiated feedback mechanisms.

Ultrastructural relationships of serotonin axon terminals in the cerebral cortex of the adult rat

PAP immunocytochemistry with an antiserum against serotonin (5-HT)-glutaraldehyde-protein conjugate (kindly donated by M. Geffard) was used to analyze the ultrastructural relationships of 5-HT axon terminals (varicosities) in the frontal (Fr1-Fr2), parietal (Par1), and occipital (Oc1M-Oc2) cortex of adult rats. One hundred-forty-five immunostained varicosities from Fr1-Fr2 (54 from layers I-II; 91 from layer VI) and 97 each from the upper layers (I-II) of Par1 and OcM1-Oc2 were examined in groups of serial thin sections (mean number of sections in series: 3.2 to 7.3). These terminals were of comparable shape and size in the 4 cortical sectors examined, and averaged 0.66 +/- 0.2 microns in mean diameter. The proportion of varicosities engaged in synaptic contact was evaluated by linear transformation of the relationship between the frequency of observed synaptic junctions and the number of thin sections available for examination. Reliability of the sampling was evidenced by a high coefficient of correlation (r greater than 0.95) in each cortical sector. The synaptic incidence extrapolated for whole varicosities ranged from 28% (layer VI of Fr1-Fr2) to 46% (Par1), without statistically significant differences between the 4 sectors examined. The interregional mean could thus be evaluated at 38%. The synaptic 5-HT terminals always made asymmetrical junctions, which were exclusively found on dendritic spines and shafts, and appeared more frequent on spines than shafts in the deep frontal and the upper occipital cortex. In all 4 sectors, dendritic shafts and spines and other axonal varicosities were frequently encountered in the immediate microenvironment of the immunostained varicosities. It is concluded that the cortical 5-HT innervation is predominantly nonjunctional throughout the neocortex of the adult rat, which reinforces earlier views of a highly divergent afferent system with particular functional properties and perhaps capable of widespread, global and/or sustained influences in this part of the brain.

Endogenous homovanillic acid levels differ between rat and rabbit caudate, hippocampus, and cortical regions

Endogenous dopamine (DA) levels and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3MT) and homovanillic acid (HVA) were measured by high-performance liquid chromatography in the entorhinal-piriform (EnPi), cingulate (CIN), sensorimotor (SSM) and visual (VIS) cortices as well as is the caudate (CAU) and hippocampus (HIP) of Sprague-Dawley (SD) rats and New Zealand (NZ) rabbits. The DA, DOPAC and 3MT contents were similar in both species. The HVA levels however, although they followed DA distribution, were several-fold higher in NZ rabbits than in SD rats for all cortices, HIP and CAU. In addition, total metabolite contents and DA turnover (estimated from 'DA metabolite/DA' ratios) were significantly higher in NZ rabbits than in SD rats, suggesting an increased release and/or metabolism in the former species. The HVA/DA ratios were much higher for NZ rabbit regions than for SD rats, indicating an increased DA release in the former species since the DOPAC/DA ratios (index of intraneuronal degradation) were similar.

Distribution of monoamines and metabolites in rabbit neostriatum, hippocampus and cortex

The monoamines noradrenaline (NA), dopamine (DA), adrenaline (AD) and 5-hydroxytryptamine (5-HT) were assayed in the putamen (PUT), the lateral (lCAU) and medial (mCAU) portions of the caudate, the dorsal (dHIP) and ventral (vHIP) hippocampus, as well as in four cortical areas, i.e., anterior cingulate (CIN), entorhinal-piriform (EnPi), sensorimotor (SSC; somatosensory) and primary visual (VIS). The use of an HPLC procedure enabled us to perform these measurements in microdissected samples and to assay as well monoamine metabolites. The DA levels were highest in the neostriatum, moderate in the EnPi and CIN and very low in the SSC, VIS and hippocampus. The distribution of NA was more uniform, although higher concentrations were measured in the neostriatum, hippocampus and EnPi. The largest amounts of 5-HT were in the EnPi, while moderate concentrations were found in the other regions. The ratios between the neurotransmitters and their metabolites were used as an index of turnover and indicate that the terminal fields of the monoamine systems are heterogenous within the neostriatal, hippocampal and cortical subdivisions.

Monoamines and metabolites in autopsied brain tissue from cirrhotic patients with hepatic encephalopathy

Alterations in the metabolism of monoamine neurotransmitters have been proposed to be involved in the development of the hepatic encephalopathy (HE) associated with experimental and human liver failure. In order to evaluate this hypothesis, the monoamines and some of their metabolites were measured in homogenates of caudate nucleus (CAU), prefrontal (PFCo) and frontal cortex (FCo) dissected from brains obtained at autopsy from nine cirrhotic patients who had died in hepatic coma and an equal number of control subjects, free from neurological, psychiatric and hepatic disorders, matched for age and time interval from death to freezing of autopsied brain samples. Monoamine measurements were performed by high-performance liquid chromatography with ion-pairing and electrochemical detection after a simple extraction procedure. In all three regions investigated, concentrations of dopamine (DA) were unchanged in cirrhotic patients vs controls while its metabolites, 3-methoxytyramine (3-MT) and homovanillic acid (HVA) were selectively affected i.e. 3-MT was found to be increased in CAU, while HVA levels were increased in FCo and CAU. DOPAC was also found to be unchanged in CAU. Noradrenaline (NA) levels were greatly increased in PFCo and FCo of cirrhotic patients but remained unchanged in CAU. No significant differences in the concentrations of either serotonin (5-HT) or of its precursor 5-hydroxytryptophan (5-HTP) were found in any of the three regions studied. However, 5-hydroxyindoleacetic acid (5-HIAA), the major metabolite of 5-HT, was increased in PFCo and CAU of cirrhotic patients. These findings show that selective alterations of catecholamine and 5-HT systems are involved in human HE and therefore, they may play an important role in the pathogenesis of certain neurological symptoms associated with this encephalopathy.

Schizophrenia: a disease of interhemispheric processes at forebrain and brainstem levels?

The evidence is convincing that each human cerebral hemisphere is capable of human mental activity. This being so, every normal human thought and action demands either a consensus between the two hemispheres, or a dominance of one over the other, in any event integrated into a unity of conscious mentation. How this is achieved remains wholly mysterious, but anatomical and behavioral data suggest that the two hemispheres, and their respective bilateral, anatomical-functional components, maintain a dynamic equilibrium through neural competition. While the forebrain commissures must contribute substantially to this competitive process, it is emphasized in this review that the serotonergic raphé nuclei of pons and mesencephalon are also participants in interhemispheric events. Each side of the raphé projects heavily to both sides of the forebrain, and each is in receipt of bilateral input from the forebrain and the habenulo-interpeduncular system. A multifarious loop thus exists between the two hemispheres, comprised of both forebrain commissural and brainstem paths. There are many reasons for believing that perturbation of this loop, by a variety of pathogenic agents or processes, probably including severe mental stress in susceptible individuals, underlies the extraordinarily diverse symptomatology of schizophrenia. Abnormality of features reflecting interhemispheric processes is common in schizophrenic patients; and the 'first rank' symptoms of delusions or hallucinations are prototypical of what might be expected were the two hemispheres unable to integrate their potentially independent thoughts. Furthermore, additional evidence suggests that the disorder lies within, or is focused primarily through, the raphé serotonergic system, that plays such a fundamental role in consciousness, in dreaming, in response to psychotomimetic drugs, and probably in movement, and even the trophic state of the neocortex. This system is also well situated to control the dopaminergic neurons of the ventral tegmental area, thus relating to the prominence of dopaminergic features in schizophrenia; and the lipofuscin loading and intimate relation with blood vessels and ependyma may make neurons of the raphé uniquely vulnerable to deleterious agents.

Acute effects of lithium on catecholamines, serotonin, and their major metabolites in discrete brain regions

The acute effects of lithium on the central catecholamine and serotonin systems were investigated in well-defined cortical areas in the rat: the anterior cingulate cortex (CIN), the piriform-entorhinal region (PiEn), and the primary visual area (VIS) as well as in the hippocampus (HIP), the neostriatum (CPU; caudateputamen), and the olfactory bulbs (OBs). In these microdissected regions, the catecholamines noradrenaline (NA) and dopamine (DA), the indoleamine 5-hydroxytryptamine (5-HT; serotonin), as well as some of their major metabolites (3-methoxy-4-hydroxyphenylglycol; 3,4-dihydroxyphenylacetic acid; homovanillic acid; 3-methoxytyramine; 5-hydroxy-1-tryptophan; and 5-hydroxyindole-3-acetic acid) were assayed by using high-performance liquid chromatography (HPLC) with electrochemical detection. One hour after the administration of lithium chloride (2 and 10 mEq/kg; i.p.) the endogenous NA levels increased in the CIN and PiEn cortices, in the HIP, and in the CPU. The DA contents remained unchanged in the CPU, HIP, OB, and VIS cortex but were increased in the CIN and PiEn regions. These increases in cortical DA levels were accompanied by reductions in HVA and DOPAC. The levels of HVA and DOPAC but not 3-MT were also reduced in the CPU, in spite of a normal DA content. The discrepancies between changes of DA and the levels of its metabolites indicate changes in the turnover rates as well as an action of lithium on DA synthesis and/or storage in the nigrostriatal and mesocortical systems. The 5-HT contents were also increased by lithium throughout all regions, except for the OB.(ABSTRACT TRUNCATED AT 250 WORDS)